Monitoring system for identifying an operating state of a motor

1. A motor assembly comprising: a first motor and a second motor, wherein the first motor is mechanically coupled to the second motor; and a monitoring system for identifying an operating state of the first motor or the second motor, the monitoring system comprising a speed sensor for determining a speed of the first motor and providing a speed signal as a function of time in response thereto; and a processor configured to identify that the first motor is in a failed state by identifying a symmetric oscillation of the speed signal, with respect to its average value, as a function of time; or to identify that the second motor is in a failed state by identifying an asymmetric oscillation of the speed signal, with respect to its average value, as a function of time.

2. The motor assembly of claim 1 , wherein the processor comprises a first monitor, wherein the first monitor compares the speed signal to a first threshold speed, and is configured such that when the speed signal is greater than the first threshold speed, the first monitor counts up at a first count-up rate.

3. The motor assembly of claim 2 , wherein when the speed signal is less than or equal to the first threshold speed, the first monitor counts down at a first count-down rate.

4. The motor assembly of claim 2 , wherein the first monitor outputs a “false” reading when a count of the first monitor is less than a first count threshold, and a “true” reading when the count of the first monitor is greater or equal to the first count threshold.

5. The motor assembly of claim 2 , wherein the processor comprises a second monitor, wherein the second monitor compares the speed signal to a second threshold speed, and is configured such that when the speed signal is more negative than the second threshold speed, the second monitor counts up at a second count-up rate.

6. The motor assembly of claim 5 , wherein when the speed signal is more positive than or equal to the second threshold speed, the second monitor counts down at a second count-down rate.

7. The motor assembly of claim 5 , wherein the second monitor outputs a “false” reading when a count of the second monitor is less than a second count threshold, and a “true” reading when the count of the second monitor is greater than or equal to the second count threshold.

8. The motor assembly of claim 7 , wherein the first threshold speed has a first positive value with respect to an average speed of the signal and the second threshold speed has a second value that is substantially the same as the first positive value but is negative with respect to the average speed of the signal.

9. The motor assembly of claim 8 , wherein the processor is configured to determine if the speed signal varies as said symmetric oscillation or said asymmetric oscillation based on the outputs of the first and second monitors.

10. The motor assembly of claim 8 , wherein the processor identifies a symmetric oscillation of the speed signal when the readings of both the first and second monitors are simultaneously “true”.

11. The motor assembly of claim 10 , wherein the processor further comprises a counter, wherein the counter counts up when both the first and second monitors output a “true” reading, and identifies a symmetrical oscillation of the speed signal when the count of the counter exceeds a predetermined counter threshold.

12. The motor assembly of claim 1 , wherein the motor assembly comprises: a further speed sensor for determining a speed of the second motor and providing a second speed signal as a function of time in response thereto, and a processor configured to identify that the second motor is in a failed state by identifying a symmetric oscillation of the second speed signal, with respect to its average value, as a function of time; or to identify that the first motor is in a failed state by identifying an asymmetric oscillation of the second speed signal, with respect to its average value, as a function of time.

13. The motor assembly of claim 12 , further comprising: a gearbox to which the first and second motors are coupled and a shaft coupled to the first and second motors by the gearbox for enabling the first and/or second motor to drive the shaft.

14. A monitoring system for identifying an operating state of a motor, the system comprising: a speed sensor for determining a speed of a motor and providing a speed signal as a function of time in response thereto; and a processor configured to identify a symmetric and/or an asymmetric oscillation of the speed signal as a function of time; wherein the processor comprises a first monitor, wherein the first monitor compares the speed signal to a first threshold speed, and is configured such that when the speed signal is greater than the first threshold speed, the first monitor counts up at a first count-up rate.

15. A motor assembly comprising a first motor and a second motor; and a monitoring system for identifying an operating state of the first motor, the monitoring system comprising: a speed sensor for determining a speed of the first motor and providing a first speed signal as a function of time in response thereto, a processor configured to identify a symmetric and/or an asymmetric oscillation of the first speed signal as a function of time; and a further speed sensor for determining a speed of the second motor and providing a second speed signal as a function of time in response thereto, and a processor configured to identify a symmetric and/or an asymmetric oscillation of the second speed signal as a function of time.